Korean patent application No. 2008-0064270 teaches pH-sensitive metal nanoparticles and a preparation method thereof. These pH-sensitive nanoparticles are negatively charged and well dispersed under neutral or basic conditions. In contrast, when they are exposed to an acidic condition, their surface charges change positively as hydrolysis occurs. In this course, the nanoparticles aggregate, with their absorption band shifting from around 500 nm to greater than 600 nm, i.e., a red to near infrared region.
After entering the body, these pH-sensitive metal nanoparticles are dispersed in normal cells, which are neutral or alkaline, and selectively aggregate in cancer cells which have acidic pH. When irradiated onto the body, near infrared light with a wavelength of greater than 600 nm, which can deeply penetrate into the body, heats metal aggregates, thereby killing the cancer cells.
The pH-sensitive metal nanoparticles are selective for cancer cells and allow photothermal therapy, but by themselves have no therapeutic functions. Therefore, there is a need for new particles that can selectively aggregate in cancer cells and therapeutically treat cancer cells by themselves.